On 05/07/2018 02:47 PM, Sebastian Andrzej Siewior wrote:

On 2018-05-03 09:43:33 [+0200], Geert Uytterhoeven wrote:

quoted

quoted

--- a/drivers/tty/serial/sh-sci.c
+++ b/drivers/tty/serial/sh-sci.c

@@ -2516,13 +2516,12 @@ static void serial_console_write(struct console *co, const char *s,
         unsigned long flags;
         int locked = 1;

-       local_irq_save(flags);

Hence the below now runs with local interrupts enabled.

For checking port->sysrq or oops_in_progress that probably isn't an issue.
If oops_in_progress is set, you have other problems, and the race condition
between checking the flag and calling spin_lock{,_irqsave}() existed before,
and is hard to avoid.

while oops_in_progress is an issue of its own, the port->sysrq isn't
avoided by by local_irq_save(). On SMP systems you can still receive a
`break' signal on the UART and have a `printk()' issued on another CPU.

quoted

For actual console printing, I think you want to keep interrupts disabled.

why? They should be disabled as part of getting the lock and not for any
other reason.

quoted

quoted

         if (port->sysrq)
                 locked = 0;
         else if (oops_in_progress)
-               locked = spin_trylock(&port->lock);
+               locked = spin_trylock_irqsave(&port->lock, flags);
         else
-               spin_lock(&port->lock);
+               spin_lock_irqsave(&port->lock, flags);

Add

         if (!locked
                 local_irq_save(flags)

here?

So for oops_in_progress you get here with interrupts disabled. And if
not, I don't see the point in disabling the interrupts without any kind
of locking.

So I understand, the initial version of this patch was correct.

@Geert if you don't object I'll send a v3 (v1 ported to mainline).

Thanks,
Daniel